Fiber-reinforced resin materials, or “composite” materials as they are commonly known, have many applications in the aerospace, automotive, and marine fields because of their high strength-to-weight ratios, corrosion resistance, and other unique properties. Conventional composite materials typically include glass, carbon, or polyaramide fibers in woven and/or non-woven configurations. The fibers can be preimpregnated with uncured or partially cured resin to form fiber plies (often termed “prepregs”) in a raw material stage. The fiber plies can be manufactured into parts by laminating them on a mold surface. Heat and pressure can be applied to the laminated plies to cure the resin and harden the laminate in the shape of the mold. The heat and pressure can be applied with an autoclave, a heated flat or contoured forming tool, or a combination of methods including the use of a vacuum bag.
Composite parts can be formed in the above manner on both male and female tools. With male tools, the fiber plies are applied to an exterior mold surface that forms an inner mold line of the part. Adding plies to the lay-up on a male tool increases the thickness of the part and changes the outer mold line, but the inner mold line remains unchanged. Conversely, with female tools, the fiber plies are applied to an interior mold surface that forms an outer mold line of the part. Adding plies to the lay-up on a female tool increases the thickness of the part and changes the inner mold line, but the outer mold line remains unchanged.
One problem that arises when manufacturing composite parts with tools including female cavities, however, is that composite materials tend to have defects (e.g., bridging, resin richness, etc.) at transition areas or internal radii on the tooling surface. Bridging, for example, occurs when the fiber plies span across the internal radii of the female tool instead of fitting flush against these contour areas of the tool surface. Resin richness results from excess resin migration to the outsides of bends, curves, and other radius or joggle areas of the composite structure.
FIG. 1, for example, illustrates a cross-sectional end view of a composite material 110 (e.g., fiber plies or prepregs) laid up on a portion of a female tool 100 in accordance with the prior art. The female tool 100 can include a mold surface 102 having a channel 103 with internal radii or transition regions 107 and external shoulder regions 109. A pressing member 120 is positioned over the composite material 110. As the pressing member 120 is moved toward the female tool 100 (as shown by arrows A), the pressing member moves the composite material 110 firmly against the mold surface 102. One problem with this arrangement, however, is that when the composite material 110 is not formed completely into the mold surface 102, bridging can occur between the composite material and the mold surface at the transition regions 107. Moreover, the shoulder areas 109 of the mold surface 102 are particularly susceptible to resin richness. As discussed above, bridging and resin richness can reduce the fiber density in the affected regions and, accordingly, compromise the structural integrity of the finished part. In many cases, such defects require that the part be reworked or, in some cases, scrapped altogether.
One approach for addressing this drawback with female tools is to use a vacuum bagging process. Such a process, for example, can include positioning one or more vacuum bags (not shown) over the composite material 110 laid up on the mold surface 102 of the female tool 100. As the vacuum bags are evacuated, the outside air pressure presses the composite material 110 firmly against the mold surface 102. Vacuum bagging processes can help reduce problems with bridging and resin richness in some cases, but such processes are extremely slow and, accordingly, can significantly limit the production rate of composite parts in a commercial and/or industrial setting.